Shape and aerodynamic

[deleted783484]

Assuming all factors affecting wind resistance to be equal except shape which of the following shapes would generate the greatest terminal velocity in the experiment

a- a water droplet
b- a sphere
c- a cylinder
d- a cube

answer is A and the answer says that during free fall a liquid will deform to assume the shape of least resistance because the resistive force can deform the object. so the water droplet is the most aerodynamic.

Can someone please explain that?

Thank you!

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[Saigon]

equations for terminal velocity and drag velocity:

the question says the weight of the objects, air density, and drag coefficient are equal. so, the only thing that affects terminal velocity is the surface area of the object. the greater the object's surface area the greater the total drag force. rain drops can change shape to minimize their surface area unlike the other objects. therefore, they have the least drag force and greatest terminal velocity.

read here if you are still confused on the concept: http://study.com/academy/lesson/wha...-definition-formula-calculation-examples.html

quote from the link I just provided you with:
"Since the air drag force depends heavily on the size and shape of the object, objects with a large surface area (like a parachute) will have a much lower terminal velocity than objects with a smaller surface area (like a person falling from a plane). The weight of the object does affect the air drag force on the object and, therefore, its terminal velocity."

btw there is an "Mcat questions and answers" thread for these types of questions. here is the link: https://forums.studentdoctor.net/forums/mcat-study-question-q-a.134/

 

[deleted783484]

equations for terminal velocity and drag velocity: View attachment 214477

the question says the weight of the objects, air density, and drag coefficient are equal. so, the only thing that affects terminal velocity is the surface area of the object. the greater the object's surface area the greater the total drag force. rain drops can change shape to minimize their surface area unlike the other objects. therefore, they have the least drag force and greatest terminal velocity.

read here if you are still confused on the concept: http://study.com/academy/lesson/wha...-definition-formula-calculation-examples.html

quote from the link I just provided you with:
"Since the air drag force depends heavily on the size and shape of the object, objects with a large surface area (like a parachute) will have a much lower terminal velocity than objects with a smaller surface area (like a person falling from a plane). The weight of the object does affect the air drag force on the object and, therefore, its terminal velocity."

btw there is an "Mcat questions and answers" thread for these types of questions. here is the link: https://forums.studentdoctor.net/forums/mcat-study-question-q-a.134/

Makes sense. So since the water droplet has a smaller area it will have a lower terminal velocity.
Thank you!

 

[Saigon]

Makes sense. So since the water droplet has a smaller area it will have a lower terminal velocity.
Thank you!

No, decreased surface area means less drag and greater terminal velocity.

 

[bears1992]

Makes sense. So since the water droplet has a smaller area it will have a lower terminal velocity.
Thank you!

I have a B.S. In mechanical engineering and I don't even have the knowledge to calculate why a teardrop shape will achieve a greater terminal velocity over a sphere. There is a coefficient of drag that is known for common shapes. The lower the number, the less drag meaning the greater terminal velocity. I don't have the numbers in front of me but I do remember that a teardrop shape has less drag than a sphere.
Assuming the MCAT won't give you a wind tunnel to test out your shapes or provides you with the coefficients of drag, I would just remember that a teardrop shape has less drag than a sphere. I really can't see that as a fair game question on the MCAT though because the knowledge for that question comes from fluid dynamics which is well beyond the scope of the MCAT. Physics covers a bit of fluids but just the basics, certainly not calculating drag and aerodynamic forces.